AutoCloseable, EventStream
public final class RecordingStream extends Object implements AutoCloseable, EventStream
The following example shows how to record events using the default configuration and print the Garbage Collection, CPU Load and JVM Information event to standard out.
Configuration c = Configuration.getConfiguration("default");
try (var rs = new RecordingStream(c)) {
rs.onEvent("jdk.GarbageCollection", System.out::println);
rs.onEvent("jdk.CPULoad", System.out::println);
rs.onEvent("jdk.JVMInformation", System.out::println);
rs.start();
}
| Constructor | Description |
|---|---|
RecordingStream() |
Creates an event stream for the current JVM (Java Virtual Machine). |
RecordingStream |
Creates a recording stream using settings from a configuration. |
| Modifier and Type | Method | Description |
|---|---|---|
void |
awaitTermination() |
Blocks until all actions are completed, or the stream is closed, or the current thread is interrupted, whichever happens first. |
void |
awaitTermination |
Blocks until all actions are completed, or the stream is closed, or the timeout occurs, or the current thread is interrupted, whichever happens first. |
void |
close() |
Closes this resource, relinquishing any underlying resources. |
EventSettings |
disable |
Disables event. |
EventSettings |
disable |
Disables event with the specified name. |
void |
dump |
Writes recording data to a file. |
EventSettings |
enable |
Enables event. |
EventSettings |
enable |
Enables the event with the specified name. |
void |
onClose |
Registers an action to perform when the stream is closed. |
void |
onError |
Registers an action to perform if an exception occurs. |
void |
onEvent |
Registers an action to perform on all events matching a name. |
void |
onEvent |
Registers an action to perform on all events in the stream. |
void |
onFlush |
Registers an action to perform after the stream has been flushed. |
boolean |
remove |
Unregisters an action. |
void |
setEndTime |
Specifies the end time of the stream. |
void |
setMaxAge |
Determines how far back data is kept for the stream. |
void |
setMaxSize |
Determines how much data is kept for the stream. |
void |
setOrdered |
Specifies that events arrives in chronological order, sorted by the time they were committed to the stream. |
void |
setReuse |
Specifies that the event object in an EventStream.onEvent(Consumer) action can be reused. |
void |
setSettings |
Replaces all settings for this recording stream. |
void |
setStartTime |
Specifies the start time of the stream. |
void |
start() |
Starts processing of actions. |
void |
startAsync() |
Starts asynchronous processing of actions. |
boolean |
stop() |
Stops the recording stream. |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
onMetadata
public RecordingStream()
IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed)SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")
public RecordingStream(Configuration configuration)
The following example shows how to create a recording stream that uses a predefined configuration.
var c = Configuration.getConfiguration("default");
try (var rs = new RecordingStream(c)) {
rs.onEvent(System.out::println);
rs.start();
}
configuration - configuration that contains the settings to use, not null
IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed)SecurityException - if a security manager is used and FlightRecorderPermission "accessFlightRecorder" is not set.public EventSettings enable(String name)
If multiple events have the same name (for example, the same class is loaded in different class loaders), then all events that match the name are enabled. To enable a specific class, use the enable(Class) method or a String representation of the event type ID.
name - the settings for the event, not null
null
public void setSettings(Map<String,String> settings)
The following example records 20 seconds using the "default" configuration and then changes settings to the "profile" configuration.
Configuration defaultConfiguration = Configuration.getConfiguration("default");
Configuration profileConfiguration = Configuration.getConfiguration("profile");
try (var rs = new RecordingStream(defaultConfiguration)) {
rs.onEvent(System.out::println);
rs.startAsync();
Thread.sleep(20_000);
rs.setSettings(profileConfiguration.getSettings());
Thread.sleep(20_000);
}
settings - the settings to set, not null
public EventSettings enable(Class<? extends Event> eventClass)
eventClass - the event to enable, not null
null
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event
public EventSettings disable(String name)
If multiple events with same name (for example, the same class is loaded in different class loaders), then all events that match the name are disabled. To disable a specific class, use the disable(Class) method or a String representation of the event type ID.
name - the settings for the event, not null
null
public EventSettings disable(Class<? extends Event> eventClass)
eventClass - the event to enable, not null
null
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event
public void setMaxAge(Duration maxAge)
To control the amount of recording data stored on disk, the maximum length of time to retain the data can be specified. Data stored on disk that is older than the specified length of time is removed by the Java Virtual Machine (JVM).
If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely if events are on
maxAge - the length of time that data is kept, or null if infiniteIllegalArgumentException - if maxAge is negativeIllegalStateException - if the recording is in the CLOSED statepublic void setMaxSize(long maxSize)
To control the amount of recording data that is stored on disk, the maximum amount of data to retain can be specified. When the maximum limit is exceeded, the Java Virtual Machine (JVM) removes the oldest chunk to make room for a more recent chunk.
If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely.
The size is measured in bytes.
maxSize - the amount of data to retain, 0 if infiniteIllegalArgumentException - if maxSize is negativeIllegalStateException - if the recording is in CLOSED statepublic void setReuse(boolean reuse)
EventStreamEventStream.onEvent(Consumer) action can be reused. If reuse is set to true, an action should not keep a reference to the event object after the action has completed.
setReuse in interface EventStream
reuse - true if an event object can be reused, false otherwisepublic void setOrdered(boolean ordered)
EventStreamsetOrdered in interface EventStream
ordered - if event objects arrive in chronological order to EventStream.onEvent(Consumer)
public void setStartTime(Instant startTime)
EventStreamThe start time must be set before starting the stream
setStartTime in interface EventStream
startTime - the start time, not null
public void setEndTime(Instant endTime)
EventStreamThe end time must be set before starting the stream.
At end time, the stream is closed.
setEndTime in interface EventStream
endTime - the end time, not null
public void onEvent(String eventName, Consumer<RecordedEvent> action)
EventStreamonEvent in interface EventStream
eventName - the name of the event, not null
action - an action to perform on each RecordedEvent matching the event name, not null
public void onEvent(Consumer<RecordedEvent> action)
EventStream To perform an action on a subset of event types, consider using EventStream.onEvent(String, Consumer) and EventStream.onMetadata(Consumer) as it is likely more performant than any selection or filtering mechanism implemented in a generic action.
onEvent in interface EventStream
action - an action to perform on each RecordedEvent, not null
public void onFlush(Runnable action)
EventStreamonFlush in interface EventStream
action - an action to perform after the stream has been flushed, not null
public void onClose(Runnable action)
EventStreamIf the stream is already closed, the action will be performed immediately in the current thread.
onClose in interface EventStream
action - an action to perform after the stream is closed, not null
public void onError(Consumer<Throwable> action)
EventStreamIf an action is not registered, an exception stack trace is printed to standard error.
Registering an action overrides the default behavior. If multiple actions have been registered, they are performed in the order of registration.
If this method itself throws an exception, resulting behavior is undefined.
onError in interface EventStream
action - an action to perform if an exception occurs, not null
public void close()
AutoCloseabletry-with-resources statement.close in interface AutoCloseable
close in interface EventStream
public boolean remove(Object action)
EventStreamIf the action has been registered multiple times, all instances are unregistered.
remove in interface EventStream
action - the action to unregister, not null
true if the action was unregistered, false otherwisepublic void start()
EventStreamActions are performed in the current thread.
To stop the stream, use the EventStream.close() method.
start in interface EventStream
public void startAsync()
Actions are performed in a single separate thread.
To stop the stream, use the close() method.
The following example prints the CPU usage for ten seconds. When the current thread leaves the try-with-resources block the stream is stopped/closed.
try (var stream = new RecordingStream()) {
stream.enable("jdk.CPULoad").withPeriod(Duration.ofSeconds(1));
stream.onEvent("jdk.CPULoad", event -> {
System.out.println(event);
});
stream.startAsync();
Thread.sleep(10_000);
}
startAsync in interface EventStream
IllegalStateException - if the stream is already started or closedpublic boolean stop()
Stops a started stream and waits until all events in the recording have been consumed.
Invoking this method in an action, for example in the onEvent(Consumer) method, could block the stream indefinitely. To stop the stream abruptly, use the close() method.
The following code snippet illustrates how this method can be used in conjunction with the startAsync() method to monitor what happens during a test method:
AtomicBoolean socketUse = new AtomicBoolean();
try (var r = new RecordingStream()) {
r.setMaxSize(Long.MAX_VALUE);
r.enable("jdk.SocketWrite").withoutThreshold();
r.enable("jdk.SocketRead").withoutThreshold();
r.onEvent(event -> socketUse.set(true));
r.startAsync();
testFoo();
r.stop();
if (socketUse.get()) {
r.dump(Path.of("socket-events.jfr"));
throw new AssertionError("testFoo() should not use network");
}
}
true if recording is stopped, false otherwiseIllegalStateException - if the recording is not started or is already stoppedpublic void dump(Path destination) throws IOException
The recording stream must be started, but not closed.
It's highly recommended that a max age or max size is set before starting the stream. Otherwise, the dump may not contain any events.
destination - the location where recording data is written, not null
IOException - if the recording data can't be copied to the specified location, or if the stream is closed, or not started.SecurityException - if a security manager exists and the caller doesn't have FilePermission to write to the destination pathpublic void awaitTermination(Duration timeout) throws InterruptedException
EventStreamawaitTermination in interface EventStream
timeout - the maximum time to wait, not null
InterruptedException - if interrupted while waitingpublic void awaitTermination() throws InterruptedException
EventStreamawaitTermination in interface EventStream
InterruptedException - if interrupted while waiting
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/jdk.jfr/jdk/jfr/consumer/RecordingStream.html